A recent study in the United Kingdom provides strong evidence that well-organized activities outside the classroom contribute significantly to the quality and depth of children's learning, including their personal, social, and emotional development. Outdoor math trails supply further evidence of such enhanced learning. This article focuses on the creation, implementation, and the benefits of math trails to students. The math trail concept was first developed by Australian educator Dudley Blaine to promote active, meaningful mathematics learning beyond the classroom. Math trails are meaningful, stimulating, challenging, and exciting for children. Most important, these trails invite "all" students, irrespective of their classroom achievement level, to participate successfully in the problem activities and gain a sense of pride in the mathematics they create. As youngsters discover real-world shapes, patterns, numbers, data, symmetry, and reflections--to name just a few examples--their eyes open to the mathematics in their world. They become math detectives--posing questions and solving problems as well as documenting and communicating their discoveries in multiple ways. The authors present an excerpt from a student-generated math trail. (Contains 2 figures.) [Additional trail examples accompany the online version of this article in an appendix at www.nctm.org/tcm.]